1. Field of the Invention
The present invention relates to failure detection for a variable valve timing and lift control system of an internal combustion engine.
2. Description of the Related Art
To achieve improvements in power output and fuel economy (gas mileage), reduction in exhaust emissions, increase in torque at low revolutions, and higher output power at high-revolution/high-load operation of an internal combustion engine, a variable valve timing and lift control system is known which changes the open/close timing and/or the lift amount of the intake/exhaust valve.
Japanese Patent No. 2943042 discloses a technique for performing failure detection of such a variable valve timing and lift control system. In this technique, frequency components associated with seating sound of the valve are extracted from an output of a vibration sensor that detects the vibration of an internal combustion engine for detecting failure of the variable valve timing and lift control system. In this technique, a pulses A and B are generated, pulse A being high level at nearly the valve close time of a high speed cam of the variable valve timing and lift control system and pulse B being high at nearly the valve close time of a low speed cam. Components of the seating sound of the valve are extracted when these pulses are at high level. By comparing intensities of these components of seating sound, the cam with a higher intensity is assumed to be the cam being controlled. Then, the variable valve timing and lift control system is diagnosed by comparing the assumed cam with the cam being actually controlled.